1. Field of the Invention
The present invention relates to a method for manufacturing piezoelectric components in which electrodes are formed on a surface of a piezoelectric substrate by a thin-film deposition technique such as a sputtering and a vacuum evaporation technique.
2. Description of the Related Art
When manufacturing piezoelectric components such as a dual-mode filter utilizing a thickness-longitudinal-vibration mode, which has complex-shaped electrodes, such as vibration electrodes, input-output-terminal electrodes, lead electrodes, and relay-capacitance electrodes, the electrodes are formed on a surface of a piezoelectric substrate by first applying an electrode material on the entire surface of the substrate by sputtering or vacuum evaporation, and then etching the electrode material via photolithography to form the electrodes. However, a large number of steps are required to complete the etching using photolithography, and thus, the manufacturing costs increase.
A method for applying an electrode material on the substrate using a hard mask requires fewer steps than the etching process and is also less expensive. However, when forming an electrode with a complex shape, the shape of the opening in the hard mask also is complex which reduces the strength of the hard mask. Therefore, the hard mask deforms due to the heat produced during adhesion of the electrode material such that a space is formed between the hard mask and the substrate which allows the electrode material to flow into the space, and thus the accuracy of the electrode pattern is greatly reduced.
As a solution to this problem, the use of divided hard masks, in which an electrode shape is divided into two or more patterns, has been proposed in Japanese Unexamined Patent Application Publication No. 11-297471.
However, for the piezoelectric components, the electrode-forming method using the divided hard masks has not been utilized for the following reasons.
At the divided portion of the electrode pattern, the electrode materials are built up for preventing wire breaking of the electrode. However, in the case of the piezoelectric components, electrical characteristics of the piezoelectric component deteriorate due to the position of the built up portion on the substrate, i.e., the electrode portion with a thickness larger than others.
In order to overcome the above-described problems, preferred embodiments of the present invention provide a method for manufacturing piezoelectric components utilizing a plurality of divided hard masks to form an electrode pattern with high accuracies while improving the strength of the hard mask and not degrading electric characteristics of the piezoelectric component.
According to a preferred embodiment of the present invention, a method for manufacturing piezoelectric components, in which a vibration electrode, terminal electrodes, and lead electrodes for connecting the vibration and terminal electrodes are formed on a piezoelectric substrate by a thin-film deposition technique, the method including the steps of preparing a first hard mask having openings corresponding to the vibration electrode and lead electrodes, preparing a second hard mask having openings corresponding to at least the terminal electrodes, continuously forming the vibration electrode and lead electrodes by the thin-film deposition technique while arranging the first hard mask on the piezoelectric substrate, and forming at least the terminal electrodes by the thin-film deposition technique while arranging the second hard mask on the piezoelectric substrate, wherein the first and second hard masks are arranged such that the openings of the first and second hard masks are partially overlapped, and wherein the overlapped portion of the first and second hard masks is located at a position on one of the lead electrode and the terminal electrode, the position being spaced from the vibration electrode by at least about three times the thickness of the piezoelectric substrate.
First, the first hard mask having openings corresponding to the vibration electrode and the lead electrodes and the second hard mask having openings corresponding at least to the terminal electrodes are prepared. The openings formed on the first hard mask extend continuously from the vibration electrode toward the entire or a portion of the lead electrodes. The openings formed on the second hard mask correspond at least to the terminal electrodes and may continuously extend along a portion of the lead electrodes. The openings formed on the divided hard masks have a simple or small area configuration to prevent a reduction in the strength of the hard mask.
Next, the first hard mask is arranged on the piezoelectric substrate, on which no electrode is formed, so as to continuously form the vibration electrode and the lead electrodes thereon by the thin-film depositing technique, such as a sputtering and vacuum evaporation technique. During the thin-film depositing, heat is applied to the hard mask, however, since the hard mask has increased strength as mentioned above, a highly accurate electrode pattern is formed.
Then, the second hard mask is arranged on the piezoelectric substrate, on which the vibration electrode and the lead electrodes are formed, so as to form at least the terminal electrodes by the thin-film depositing technique in the same manner. At this time, to prevent wire breakage, the lead electrodes formed by the first hard mask are partially overlapped on the terminal electrodes or a portion of the lead electrodes formed by the second hard mask so as to increase the thickness of the electrodes. Since the overlapped portion, however, is located at a position spaced from the vibration electrode preferably by about three times or more than the thickness of the piezoelectric substrate, the piezoelectric vibration produced by the vibration electrode is not adversely affected by the overlapped portion, thus, preventing characteristic degradation caused by unnecessary vibration or reflection waves.
Adhesion of an electrode material to a portion of a piezoelectric component which does not require it directly produces deterioration of electrical characteristics, such that accuracy in electrode configuration is demanded. When using the divided hard masks, the second or later-used hard mask is spaced from the substrate due to the thickness of the previously applied electrode material so as to produce a clearance between the hard mask and the substrate. When the electrode material extends into the clearance, blurring or deformation in shape of a finished electrode is produced which causes characteristic degradation.
Preferably, a contact surface between the surface of the piezoelectric substrate and the second hard mask includes a concave portion formed to accommodate the vibration and lead electrodes formed using the first hard mask.
That is, when the second hard mask is arranged on the piezoelectric substrate, the vibration and lead electrodes are located within the concave portion formed on the second hard mask to prevent the second hard mask from being spaced from the piezoelectric substrate. Accordingly, when forming the terminal electrodes and lead electrodes, the blurring or deformation in shape of the electrodes is prevented from occurring, and thus characteristic degradation is prevented.
In addition, the order of forming electrodes on the piezoelectric substrate is not limited to the above-described procedure. Alternatively, the terminal electrodes and the lead electrodes may be formed using the second hard mask before the vibration electrodes are formed using the first hard mask.
Then, preferably, a contact surface between the surface of the piezoelectric substrate and the first hard mask is provided with a concave portion formed to accommodate the terminal and lead electrodes formed using the second hard mask.
When the lead electrode includes a curved portion at an intermediate portion thereof, the divided portion is the curved portion of the lead electrode, such that the opening shape is simplified. That is, preferably, the openings of the first hard mask extend from the vibration electrode to a position corresponding to the curved portion of the lead electrode, and the openings of the second hard mask extend from the terminal electrode to a position corresponding to the curved portion of the lead electrode.
When the lead electrode has a straight shape, preferably, the openings of the first hard mask extend from the vibration electrode to positions corresponding to the connection portions of the lead electrodes to the terminal electrodes, and the openings of the second hard mask correspond only to the terminal electrodes. In this case, the terminal end of the lead electrode is overlapped on the terminal electrode.
The divided portion is preferably located on the lead electrode when using divided hard masks for the following reasons. When the divided portion is located on the terminal electrode, an opening extending from the vibration electrode to a portion of the terminal electrode via the lead electrode on the piezoelectric substrate would be required, such that the opening configuration of the first hard mask is complicated, resulting in a substantial reduction in the strength of the first hard mask. Similarly, when the divided portion is located on the vibration electrode, an opening extending from the terminal electrode to a portion of the vibration electrode via the lead electrode on the piezoelectric substrate would be required, such that the opening configuration of the second hard mask is complicated, resulting in a substantial reduction in the of the second hard mask. Such a problem becomes noticeable especially when a curved portion is provided on the lead electrode. Furthermore, when the divided portion is located on the vibration electrode, the vibration electrode is partially changed in thickness which adversely influences the vibration characteristics. Therefore, it is preferable that the divided portion be located on the lead electrode.
In addition, the width of the lead electrode is small, approximately 0.2 mm, for example. However, since accuracies in the size of the openings of the hard mask and in the positioning of the hard mask are greatly improved in preferred embodiments of the present invention, there are no problems with the accuracy of the lead electrodes.
As described above, according to preferred embodiments of the present invention, since an electrode pattern is formed on the piezoelectric substrate using a plurality of separate hard masks, the configuration of openings formed on each hard mask is greatly simplified so as to form a high-accuracy electrode pattern by preventing the reduction in strength of the hard mask.
Also, after forming the vibration electrodes and lead electrodes (or the terminal electrodes and lead electrodes) on the piezoelectric substrate using the first (or second) hard mask, the terminal electrodes and lead electrodes (or the vibration electrodes and lead electrodes) are continuously formed on the piezoelectric substrate using the second (or first) hard mask, while the terminal electrode or a portion of the lead electrode formed by the second (or first) hard mask is overlapped on the lead electrode formed by the first (or second) hard mask, such that wire breakage does not occur in a lead electrode portion so as to connect the electrodes securely.
Furthermore, because the overlapped portion of the electrodes is located at a position that is spaced from the vibration electrode by about three times or more than the thickness of the piezoelectric substrate, the piezoelectric vibration caused by the vibration electrodes is not adversely affected by the overlapped portion, thereby preventing characteristic degradation due to unnecessary vibration or reflection waves.
Other features, elements, characteristics and advantages of the present invention will become more apparent from the following description of preferred embodiments thereof with reference to the attached drawings.